x86 boot code build

[Konstantin Belousov]

On Fri, Oct 05, 2012 at 03:22:31PM +0200, Dag-Erling Sm??rgrav wrote:
> Konstantin Belousov <kostikbel at gmail.com> writes:
> > So what ISA additions do you expect to get advantage of by switching
> > to pentium-mmx from 486 ? As I already said, I am not aware of any.
> 
> The TSC, for one.  MMX, and the ability to use MMX registers to copy
> data.

TSC is used regardless of the compiler flags, we use it if CPU claims
that TSC is supported, even in usermode.

Compiler never generates MMX copies. More, in kernel, the manual
FPU context save/restore is needed around the FPU/MMX register file access.
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